Previous transmission electron microscopic (TEM) investigations of cellular cementum in man and other species have suggested that while the most superficially positioned cementocytes exhibit the ultrastructural characteristics of vital cells, those located more deeply appear to be dead or moribund. We have demonstrated, using a scanning electron microscopic (SEM) cast technique, that a continuous canalicular network often exists throughout the full thickness of cellular cementum in man. Prior to these observations it was not known whether the canalicular network in cementum formed a continuous system such as that seen in bone. A continuous system offers the potential, at least, for vital cells to be maintained in deeper portions of the tissue. We believe that the failure to demonstrate this vitality is related to the inherent difficulty in fixing a tissue whose cells are entrapped in a mineralized matrix. Previous investigators simply immersed intact roots in the fixative; thus, the only route for diffusion of the fixative was via canaliculi which opened into the surface of the cementum. We have developed a saw-microtome technique whereby unfixed tissue can be rapidly cut prior to fixation. This technique will be used to cut 100-300 um longitudinal sections through the roots of newly-extracted human molars and perfusion-fixed rat molars. Sections from the human molars will immediately be cut into smaller segments with a heavy gauge razor blade. Sections prepared in this manner have exposed canaliculi on five surfaces of the tissue. These sections are within the well-established dimensional size range for optimal ultrastructural presentation of cells. Immediately after sectioning, the sections will be placed in a rapidly-penetrating fixative. Some of the sections will be decalcified, post-fixed and embedded in a low viscosity resin. Sections from rat molars will be prepared and processed in a similar manner. The functions of the cells entrapped within the matrices of mineralized tissues such as bone and cellular cementum still remain an enigma. We believe that the fixation protocol outlined in the proposed investigation will reveal more accurately the ultrastructure, and therefore the functions, of these cells.